Recent innovations have made high speed ships a reality. Semisubmerged ships of the types described in U.S. Pat. Nos. 3,623,444 and 3,730,123 are capable of sustained high speed operation, yet they tend to be vulnerable to the effects of unusually high waves. When unusually high waves strike their relatively large platforms, the slamming loads might deform the underside plates. Even the well known catamaran-type vessel is subject to such battering when waves hit the underside of the structure bridging the two hulls. As with the semisubmerged ship design, the impacting forces not only damage the boat but buffet the occupants and anything on board. Such abuse is reduced by slowing the rate of travel, but this precautionary step compromises these ships' high speed capability. One noteworthy attempt to remedy this unsatisfactory situation is disclosed in U.S. Pat. No. 3,842,772 issued to Thomas G. Lang entitled "High Speed Ship with Bow Impact Alleviator." This patent discloses, among other things, cusp shaped projections on the underside of the platform which hydrodynamically cooperate with impacting waves to create internal tensile stresses. This design did lessen the effect of the slamming waves and has been incorporated into a prototype currently undergoing extensive testing and evaluation. To date, there have been indications that additional compensation for the slamming effect of large waves may be desirable. Thus, there is a continuing need in the state of the art for structural modifications for a semisubmerged ship or a catamaran type craft which reduces the effect of impacting waves, yet does not overly add to the vessel's weight or bulk.